body {
  font-family: 'Arial', sans-serif;
  margin: 0;
  padding: 0;
  background-image: url(../images/背景图.jpg);
  background-size: cover;
  background-attachment: fixed;
  background-repeat: no-repeat;
  background-position: center;
  overflow-x: hidden;
  margin-top: 50px;
}

header {
  color: #7fe9e9;
  padding: 10px 0;
  font-size: 20px;
  position: relative;
  width: 100%;
  top: 0;
  z-index: 1000;
}

nav {
  text-align: center;
  margin-top: 5px;
}



footer {
  color: #7fe9e9;
  text-align: center;
  padding: 10px 0;
  position: relative;
  bottom: 0;
  width: 100%;
}

footer span {
  font-size: 12px;
}